a) Field of the Invention
The present invention relates to reticles, semiconductor wafers, and semiconductor chips, and more particularly to reticles, semiconductor wafers and chips suitable for measuring the widths of circuit patterns.
b) Description of the Related Art
Recent design rules for highly integrated circuit devices use circuit patterns having a width of submicron order. In order to reliably manufacture integrated circuit devices having patterns of submicron order, it is essential to make precise measurements of pattern widths. Each pattern width is measured, for example, after a reticle is formed, or during the manufacture processes of integrated circuit devices, the widths of resist patterns and circuit patterns formed at photolithography and etching processes are also measured before proceeding the next manufacture process.
FIG. 7 is a schematic diagram showing the structure of a reticle line width measuring apparatus. Illumination light 50 passes through a condenser lens 51 and illuminates a reticle placed on a reticle stage 52. A pattern formed on the reticle is enlarged by an optical system composed of an objective lens 53, a relay lens 54, a mirror 55, an image rotator 56, a relay lens 57, mirrors 58 and 59, and a relay lens 60, and is focussed onto a slit mirror 61. The magnification factor of this optical system is, for example, about 80.
The reticle stage 52 can move the reticle in a plane (x-y plane) parallel to the reticle surface. By moving the reticle in the x-y plane, a desired pattern formed on the reticle can be focussed on a slit mirror 61. An image formed on the slit mirror 61 can be observed through another optical system 63.
The slit mirror 61 is formed with one slit extending in the vertical direction. Light passed through this slit is converted into an electrical signal by a photomultiplier 62. While the slit mirror 61 and photomultiplier 62 are scanned in the horizontal direction along the focus plane, electrical signals having an intensity corresponding to dark/blight areas of an enlarged image of the reticle pattern are obtained.
If the enlarged image of a straight line pattern and the slit are parallel, the pattern width can be calculated from the obtained electrical signals. If the enlarged image of a straight line pattern and the slit are not parallel, the image rotator 56 is rotated about its rotary axis to rotate the enlarged image and align the pattern image and slit in parallel.
A pattern parallel to or perpendicular to a reference line of a reticle used for stepper position alignment easily forms an image parallel to the slit of the slit mirror shown in FIG. 7. However, in order to measure the width of a line oblique to the reference line, it is necessary to rotate the image rotator 56 to make the enlarged image of the line in parallel to the slit.
The image rotator 56 is rotated while an operator views the enlarged pattern image through the optical system 63. If the relationship between the enlarged pattern image and the slit is shifted from parallelism, it is not possible to measure a correct line width. The measured width of an oblique pattern may change with each operator depending upon the measurement skill and the like. Even if the same operator measures, the measured results may change at each measurement.